Moz

promobricks, more than 30s of your 90s video is your splash screen. Don't you thinks that's kind of excessive?

Going off the size ratio between the motor, other elements and the propellers, I want to know which Lego props they're using. And what voltage they're feeding into that M motor. I suspect if you overvolt it it would work for a while. Freeze it overnight in a plastic bag, whip it out of the freezer, pump 30 volts into it... lots of power. Stability could possibly be achieved by the limited flexibility of the power cord. All you need is surplus lift. Think of it like the tail on a kite.

I think you'll get slightly under half a stud of extension, because any slope on the axles means the worm will slide to the bottom.

DrJB: Yes, but you could use 3 long pins with friction in an "illegal" way and it would work. TLG designed wouldn't be allowed that, but you can. And 3L pins are cheap enough that even if you do trash them after they've been like that for a few weeks it's no great loss. The extra bit sticking out could be used to hold something decorative :) Or just 3L axles with half bushes each side to hold them in place.

rambambulli, your project is a good start, don't get me wrong. Especially now that you have the parts, it's worth completing it. And you will get the phone-control part, which is what many people want. You could even build it into many models and phone-control it. My personal issue here is that I don't want to start down the "looks like Lego" path if I can avoid it. In many ways the whole point is to work within the limitations of the medium, I've build computer-controlled machines and radio controlled toys before, but both of those are really, really expensive hobbies. Lego is cheap by comparison, but only if I stick to Lego. As soon as I start saying "add some electronics and..." the money starts evaporating. And getting a compact circuit board with big enough driver transistors to handle, say, 4 XL motors, plus a battery, built into a Lego-compatible box is not going to be cheap. I can get the proto 3D printed, and DIY the first circuit, but then.... what? Suddenly I'm spending lots of time, and lots of money, manufacturing hardware. Again. My partner would kill me. Again :)

I wasn't going to use them with Lego at all, I bought them for the BLE as a sensor platform. I have a project where I'd like a network of environmental sensors, powered by little solar panels and ideally not wired. So the one-chip BLE setup in the RFduino seemed like a good easy way to start playing with mesh networks. But there is at least one board that will deal with large currents, so I could see how it copes with an XL motor. I'm actually thinking of doing a basic feedback setup using an analogue input and switching the output to get PWM, but I'll have to see whether it works at all first :) For me, the goal is something compact and RF based, because IR is annoying with larger models and at exhibitions. I'd also like better control than the Lego IR gives, and ideally the ability to run off a 4S lithium pack so I can always supply 9V to the motors. That doesn't seem impossible to me, and with an Arduino you've got so much processing power available that that part of it is a bit of a joke. You could run a FSM looking at 4 outputs and 4 inputs at 100kHz or more, on a few mW. Driving the output transistors would actually be your major power cost. But not this week, I'm kinda busy.

I was hoping you'd go the other way, and use BLE to talk to an Arduino in the Lego-compatible controller brick. But this is a much easier first step, especially for someone with no electronics experience. I have a pile of RFduino stuff here that could form the basis of a compatible kit, I should play with that. Hmm.

It looks as though the middle wheel is on a trailing arm that can move out of line a little. Or possibly the two front wheels are on a pivoting bogie. Remember that motorbikes don't usually steer much, they lean. And a display bike like this doesn't have to ride well, it just has to be rideable at all. I'd be more concerned about driving up ramps and kerbs, where it would be easy to unweight the middle wheel just as you want to apply power. Trucks get stuck like this occasionally, where a 6x2 truck going up a ramp will have to hit the start quite fast to avoid having the driven wheels in the gutter while the weight is on the outside wheels. Or go up at an angle, but that's not always possible.

The big issue with helical gears and Lego is that there's a lot of sliding, which is not kind to unlubricated plastic. The current worm gear demonstrates that and the angle issue described by DrJB above. For any high-load application you end up having to put grease on the model.

The review actually says "Keep an eye out at Lego online also as all 20,000 have not been released yet.". Which seems to be accurate - not every set has been sold, there are 20,000 in total. I don't think he's right about whining to managers at Lego shops being the way to get one, though.

Weird, there seem to be quite a lot of other not-strictly-Lego things with "Lego" in the name (compatible parts, chromed parts, other instructions) so it doesn't seem that that one set of instructions stands out. I wonder if it was a complaint by some random that sparked this?

Maybe add a couple of shock absorbers where the rear rams go? That way the arm compresses them when it is at its lowest position and they help raise it back up.

Years ago when the 8880 supercar was going out of production I got I think five of them for about $US100 each via Fredrick Glockner in Norway. Some big toy shop there had a stack of them very cheap. I was very happy, they sold for over $US200 in NZ when we could find them. Mind you, I got a couple of the same-era space shuttle for ~$US100 each in a department store sale - I don't think they knew what to do with them.

Don't forget the financial strain a lot of people are under - that means there are more sets available, which drives prices down.

The smiley face box trailer still shames me. It was thrown together quickly to go with the 8871 you can see there. I was part way into designing a rounded section for an unrelated project when I got asked for the truck/trailer for a display. For some bizarre reason I looked at the curve and thought "trailer with rounded front", so I built it. Then because I was insane, I put the smiley face on the side. I'm not sure this even qualifies as a technic model...

I like the model, it's really realistic and I'm impressed that you've managed to motorise so much of it. I like the linking oof the three gearbox elements, that's such a simple and obvious thing (but hard to arrange in many models). Your steering is also cunning. Any chance of a video? Yes, the google folder works for me. But the image links don't, I suspect because google have worked hard to break deep linking.

Brilliant! Not necessarily in a good way, but brilliant nonetheless :)

Zazck, people from TLG read these forums... and I suspect anyone even slightly familiar with Technic would say "so don't do that". Challenge: what's the earliest date at which an Impossible Lego could have been made? Viz, all the parts were available in released sets. I'm thinking a 4x6 brick open centre with two axle and pin connectors inside, held to each other by a technic pin then a 2 long axles in from each end. That's pre-2001, at least. But I suspect that a 3D cube made from 8x1 technic bricks, pins and axles could be made impossible to disassemble.

I don't think that's any different to the non-Lego tyres and the various online shops selling non-Lego or modified bricks. We regularly see people winning awards and getting featured on blogs with models that have a lot of those things in them (the number of chromed parts in some trucks, for example, is ridiculous). Technic builders to that almost as much as the custom minifig crowds do. One example I've experienced is Brickvention in Melbourne explicitly saying that anything that looks like Lego is acceptable.

Problem is that wheeled excavators usually have bigger wheels than the truck you're building. And the walking/tracked ones are ridiculously large. Maybe one of the "really big crane" guys?

Why do you take them apart for that? I just use a bath ot laundry sink that's deep enough/big enough for the model and wash it that way. Or the shower, if I'm really desperate. But do take PF elements out first :)

I assume you mean something like this: https://en.wikipedia.org/wiki/Ackermann_steering_geometry That works, especially since Lego models (and to a large extent the real truck) fit the "low speed" requirement. We also don't really care about suspension travel. The problem is steering angles/minimum turn radius. Ackermann limits this quite a lot, with flop at travel limits being a secondary concern. I think you'll struggle to get to the limit in my diagram above.

About 3:1 in the above diagram, but that's why you use one electric motor per wheel pair. The slowest wheels will almost stall, while the fastest will not provide much push. If you try to use fewer motors you will need a lot of differentials. The intermediate gearing between the diffs will produce a sort of limited slip effect which will be helpful. If you use a LA to change the leverage of the main steering LAs you should be able to halve the slip error without much work, but the mechanism I found was bulky. Getting the right part of the sine curves just with single LAs and levers was tricky, IIRC the proper lever length is about 3 studs for a 45° each way turning wheel so slop becomes a big issue. Using gears driving the turntables directly simplifies problems with extreme steering angles, but I suspect you'd want to use something like MatLab to plot the 4 steering angles vs turn radius then try to get the best straight line fit to each curve. Using gearboxes, I built one output per line then swapped them between wheelsets depending which way I was turning (ie, the left and right wheelsets swap over depending on whether they're the inside wheelset or the outside one). This could all be done entirely mathematically, and I suspect some smart person could actually derive it from first principles into a clean set of equations. Then all you need is three continuously variable, no-slip gearboxes :)

Ah, I assumed that like a lot of Technic builders you have a stack of those lying around. I have the 6-AA battery boxes in silly numbers from my road train project, since I bought several 8043 (excavator) and 8258 (crane truck) for the M motors and other parts. When I tried to sell some battery boxes off no-one was interested. I ended up buying extension leads as spare parts, that was unexpectedly expensive. Oh, and 2x2 round bricks to reduce wind-up in the axles (they make a significant difference). ?? I'm not sure why, I just built up a frame approximately the right size and mounted a single wheel under each turntable. Putting that on sheets of paper on the floor and rolling the model across it showed an awful lot of scrub no matter what I did. The "paper on the floor" trick is what I use for recumbent trikes, BTW. But that does mean you need the turntables and much of the steering mechanism worked out. Once I gave up on simple levers and started using gearing it actually got easier, because I could shift to using worm gears driving the turntables and wind-up in the axles didn't matter as much. But it meant changing gears between turning left and right, which is where the cams came in (make sure the change happened exactly straight). For a while I thought I could get crabbing by using 5 gearboxes, which I suspect is actually possible, but that was about the time I gave up. I was using simple geometric ratios, but they aren't constant over the steering angle so it all got a bit hard. I kept imagining some funky mechanical integrator arrangement that could get it right, but I'm not smart enough to work it out - I grew up with digital controllers, so I'd use maths directly. Here's what I mean by geometric - I sketched the front half of the vehicle when it was turning at twice its width (because that's easy to visualise). The grey lines intersect at the centre of the turn. I used this as my steering limit, BTW, and drew another couple of sketches at intermediate angles to see how bad the error was if I used simple, constant ratios.

It seems very symmetric to me, but since the steering lock is not great that probably will not matter. The real thing can just about pivot on the inside middle wheelset, so they use fancy computer control to get every wheel angled properly. I was trying to work out a mechanical solution for this, even approximate, but I gave up at the cam operated gearbox stage. Even disallowing crabbing, the "ackerman" compensation has to be huge on the front wheels because the width is so great compared to the turning circle (it's not quite 1:1). I wonder whether the plans for the real thing use strain guages to correct the steering angle, rather than trying to estimate suspension movement and pre-steer to compensate (as one wheel of the pair lifts the centre moves sideways, stressing the support pillar). Given the size of the truck it's not out of the question that they use live ground measurement of some sort - I haven't seen it mentioned but it seems obvious to me. And "too expensive"... from someone using 20 unimog wheels!